This application is related in subject matter to my concurrently filed application Ser. No. 791,226, filed April 27, 1977, and Ser. No. 791,227, filed Apr. 27, 1977.
This invention relates to variable speed drives. More specifically, the invention relates to a variable speed drive system for use in small riding vehicles such as riding lawn mowers, garden tractors, and the like.
A wide variety of variable speed drives for small self-propelled vehicles are available throughout the prior art. Typically, such systems comprise a small driving motor such as a gasoline engine for rotating a driving pulley. The driving pulley is coupled by a V-belt to a driven pulley which imparts rotational motion to variable speed means such as a set of planetary gears. In operation, the vehicle operator adjust the gears to select a desired rate and direction of travel, and then drivingly engages the V-belts with the pulleys to drive the vehicle. See, for example, U.S. Pat. Nos. 3,789,684; 3,311,186; and 3,575,252.
Variable speed gear assemblies for use in riding lawn mowers and other small riding vehicles have not been totally satisfactory because of their relatively high cost. Further, conventional gear assemblies do not provide continuous speed variation over a wide range of low to high speeds without shifting gears. Moreover, gear drive systems have typically utilized a single V-belt which is subjected to large starting forces upon initial engagement with the pulleys. These large starting forces often cause the vehicle to dangerously buck and jerk. The existence of large starting forces also significantly shortens the operational life of the V-belt, and thereby requires frequent belt replacement.
Some variable speed drives have been proposed using a double pulley variable speed sheave for obtaining wide range speed variation. See, for example, U.S. Pat. Nos. 3,015,237; 3,457,797; 3,470,757; and 3,583,535. The variable speed sheave is mounted between a driving pulley and a driven pulley, with a second V-belt coupling the sheave with the driven pulley. The driven pulley in turn imparts rotational motion to the vehicle wheels via chains and sprocket wheels or the like. Speed variation is obtained by shifting the variable speed sheave with respect to the other pulleys to alter the sheave drive ratio. However, in such prior art systems, it is common practice to maintain one of the V-belts under driving tension at all times and to selectively engage and disengage the other V-belt for starting and stopping of the system. Thus, upon initial motion of the vehicle, one belt is required to absorb large starting forces. Accordingly, the dangerous bucking and jerking starts inherent with single belt drive systems have not been satisfactorily eliminated.
In recent years, safety has become an increasingly important criteria in the design of riding lawn mowers and the like. Accordingly, it is highly desirable to have drive assemblies such as gears, sprocket wheels, chains, etc. inaccessibly housed for safe vehicle operations. In this regard, prior art variable speed gear assemblies are advantageous in that they are typically enclosed within a gear box. On the other hand, chains and sprocket wheels used with variable speed sheaves are often mounted in an accessible location on the underside of the vehicle. See also U.S. Pat. Nos. 3,777,585 and 3,759,342. These exposed driving elements are inherently dangerous, and are frequently involved in severe consumer accidents.
It has also become desirable for riding lawn mowers and other small riding vehicles to include a so-called dead man control for automatically and immediately disabling the vehicle drive system in the event the operator falls off the vehicle or otherwise becomes unable to properly operate the vehicle. Generally, however, prior art riding vehicles have failed to utilize such dead man controls. Instead, prior art vehicles have used conventional clutch mechanisms which are normally biased for maintaining the drive system in an engaged, operating condition. Such clutch mechanisms require positive operator action to disable the drive system, and thereby cause the vehicle to continue operation in the event the operator falls off the vehicle.
Maintenance has also become an increasingly important aspect in the design of small vehicles such as riding lawn mowers. In particular, it is well known that V-belts used in belt drive systems tend to stretch during use. Eventually, the belts stretch to an extent whereby they no longer drivingly engage their respective pulleys. To this end, it is common practice to utilize springably biased pulley-carrying arms or springably biased idler pulleys for maintaining belts under driving tension. See, for example, U.S. Pat. Nos. 3,583,535; 3,015,237; 3,457,797; and 3,470,757. However, these mechanisms serve to maintain relatively constant tension on the belts regardless of belt stretching and regardless of belt velocity during operation. However, for maximum belt operating life, it is also desirable to adjust belt tension in accordance with operating speed while simultaneously adjusting for belt stretching. Specifically, some vehicles such as riding mowers require relatively high belt tension at high horsepower, high speed operating conditions, and relatively low belt tension at low horsepower, low speed operating conditions for optimum belt life. Other types of vehicles such as some recreational vehicles require relatively high belt tension at low speeds, and relatively low belt tension at high speeds. Prior art devices which account for belt stretching have failed to satisfactorily adjust belt tension over a range of operating speeds.
The variable speed drive of this invention provides an integrated drive system for a riding lawn mower or the like which overcomes the many problems and disadvantages of the prior art. Specifically, this invention provides a variable speed sheave assembly and driving belts in a variable speed drive which smoothly starts and drives a vehicle without significant bucking or jerking, and which provides speed variations over a continuous wide range. Moreover, this invention provides a variable speed drive which has substantially enclosed and concealed driving elements, which provides an effective dead man control, and which adjusts belt tension in accordance with operating speed.